Cerebral metastases occur in cancer patients, and comprise the most common neoplasms of the brain. Patients frequently develop severe neurologic dysfunction and may die as a consequence of metastatic disease to the brain. The majority of patients undergo radiation therapy as a component of their treatment regimen. The potential efficacy of this treatment is limited to the need to avoid radiation toxicity to normal tissues. The dose of x-irradiation that can be administered is limited. Experience with large dose single fraction, whole brain x-irradiation for metastatic disease has shown this treatment method to be efficacious but with an increase in the frequency of toxicity. Pentobarbital has been shown to decrease acute radiation toxicity in the rodent whole brain x-irradiation model. To determine whether pentobarbital offers protection from radiation toxicity, and to establish whether the course of radiation therapy can be accelerated, patients will undergo high-dose, single-fraction, whole brain x-irradiation with or without pentobarbital anesthesia. The course and development of toxicity and rate of tumor control in these groups will be compared to that induced by standard radiation therapy by monitoring multiple functional and anatomic parameters before therapy and serially thereafter. If successful in reducing toxicity, this data will serve as a basis for further incremental increases in single fraction x-irradiation with the ultimate goal being better tumor control.